Overload protector



Feb. 11, 1964 M. J. LEBOW OVERLOAD PROTECTOR 2 Sheets-Sheet 1 .Filed Feb. 12, 1960 INVENTOR Mu. TON Leaow A ms (film/041v ATTORNEYS 2 Sheets- Sheet 2 M. J. LEBOW OVERLOAD PROTECTOR Feb. 11, 1964 Filed Feb. 12, 1960 IN l/ENTOR Nu. rmv J Lssow 5 0775 4: fi/m/mw ATTORNEVS United States Patent 3,120,754 OVERLOAD PROTECTOR Milton J. Lebow, Oak Park, Mich., assignor to Lebow Associates Inc., Detroit, Mich. Filed Feb. 12, 1960, Ser. No. 8,456 8 Claims. (Cl. 73141) The present invention relates to new and useful improvements in safety devices and particularly to an overload protector which is used in conjunction with a force measuring load cell.

Frequently force measuring load cells are damaged by excessive loads. Because of their high cost, it presents a serious problem.

It is therefore an object of the present invention to provide an overload device which will permit unhampered use of the load cell, while still providing an over load protector to prevent excessive loading.

Another object of the invention is the provision of an overload protector which can be used in tension or compression.

Still another object of the present invention is the provision of an overload device which can be used on very low or very high loads, the device being simple, durable and efiicient.

Another object of the present invention is the provision of an over-load safety device that can be used as a single unit or the individual units can be joined and used in tandem.

Still another object of the present invention is the provision of a device that is quickly adjustable and positive in action.

Another object of this invention is the provision of an overload safety device wherein preloaded springs cooperate to provide a low spring rate deflection and mechanical stops are provided within the assembly to carry any overload.

Still another object of the present invention is the provision of a safety device whereby the preloaded springs form a separate assembly which may be used as such.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

FIG. 1 is a cross sectional view of a single overload safety device embodying the present invention.

FIG. 2 is a cross sectional view of a tandem unit embodying the present invention.

FIG. 3 is a cross sectional view taken on lines 33 of FIG. 1.

FIG. 4 is a load deflection graph.

FIG. 5 is a modified form of the present invention.

IBefore explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to FIG. 1 of the drawings, a commercial load cell is shown mounted in a housing 20. The body of the housing is of generally cylindrical configuration. The top section 22 thereof is cut away to accommodate the irregular configuration of the load cell 10, While the lower section 24 thereof has an internal stop flange 26 integral therewith. The upper and lower flat ends 28 and 30 of the housing 20 have rigidly secured thereto, two flat end members 32 and .34. Each of the 3,120,754 Patented Feb. 11, 1964 end members being affixed with a plurality of threaded members 36 such as cap screws. The upper end member 32 is flat and formed of generally uniform thickness material and has a large threaded opening 38 located in alignment with the vertical housing axis. The threaded opening 38 therein is adapted to receive a flat threaded plug member 40'. Plug 40 also has a central opening 42 therethrough which is adapted to be concentric with threaded opening 38.

Opening 42 is adapted to receive the threaded stem member 12 which extends from the load cell 10. R0- tatably positioned on the stem member 12 are a pair of jamb nuts 14 and 16-, while immediately below threaded portion of the stem 12 is a flanged or otherwise upset portion 18. Plug 40 is locked in position with the flat locknut 44.

A hollow flanged section 52 is rigidly secured to the bottom of the load cell body 10 by means of a plurality of cap screws 54, the heads of which are recessed below the lower flat surface 58 of flange 56. The generally fiat surface 58 of the flange 56 is adapted to engage the upper inside surface 72 of the flat spring ring 70. The outer or circumferential portion of the spring ring 70 is adapted to engage flange 26, located in the housing 20.

Retainer flange is secured by screws to the lower surface 62 of the hollow flanged member 52. Flange 80 is located in horizontal spaced relationship to the spring ring 70. A plurality of locators or pilots 84 extend upwardly either from the retainer flange 80 or the spring ring 98' to position as well as center a plurality of compression springs 96 between the spring rings 70 and mounted intermediate thereof.

The lower end member 34 is positioned on the housing 20 by cap screws 36 and the central portion thereof is undercut at 46 to accommodate flange 80. The top surface of the end member 34 forms the stop flange 48 and limits the movement of spring ring 90.

The operation of the above described device will be discussed in conjunction with the operation of the modified forms of the invention, shown in FIG. 2 of the drawings.

Basically, the device illustrated in FIG. 1 is the same as the device shown in FIG. 2. However, the embodiment illustrated in FIG. 2 utilizes two of the devices shown in FIG. 1, slightly modified.

Two commercial load cells and 111 are mounted on the axis of two similar cylindrical housings and 121. The housing members, although shown of cylindri cal configuration, could of course be of many shapes and the body portion could be made up of a plurality of rib members (not shown).

Portions of the housings 120 and 121 are open at 122 and 123 to accommodate the load cells 110 and 111. The central sections of the housing bodies 124 and 125, although not integral with the housing are of the same flanged configuration as that illustrated in FIG. 1. The internal flanges 126 and 1.27 provide the stop means for the spring rings and 171. The inner spring rings 190 and 191 are positioned by the spring pilot locators 184 and 185 which are secured to the retaining flanges and 181. The retaining flanges 180 and 181 are rigidly secured to the body of the cylindrical flanged members 152 and 153 by screws 166 and 168.

In the lower unit, one row of screws 166 secures the bers are joined to the housing proper by a plurality of screws which extend therethrough. A first row of screws 136 extend upwardly through .the flange member 13 4 and the housing body 1121. A similar row of screws 137 extends downwardly through flange 135and into the housing 120 to join the lower'assembly. Both assemblies are joined by screws 176. r

The configuration of flanges 134 and 13 5 is similar to that first described. However the central portion of both flanges are raised and have threaded openings 1.8 6 and 187 therethrough. Each of the openings 186 and 187 positioning centering rods 192 and-193 which in turn center ball bushings 194 and 195. The ball bushing 194 is located in the centnal opening of the flanged member 152 in the lower unit while a second ball bushing 195 is positioned in the central opening in flanged member 153 in the lower unit. This keeps both the upper and lower in accurate alignment.

lIhe end members 132 and 13 3 are. mounted on the housing bodies 1.20 and 121. Each member 132 has mounted on its central portion a uniform thickness spacer ring 204 to which is secured a second circular ring member 205. The second circular ring member 205 has a threaded portion 206 in the center, into which a threaded flange member 207 is positioned. The flange portion 208 thereof, engages the underside 209 of the second ring member 205. The end 210 of the flanged member 207 is squared or flattened so that it can be rotated with respect to the second ring member v205, which is aflixed to the end plate 132 with a plurality of screws 213.

A flanged stem member 112 extends from the load cell 110. The flanged portion 101 of stem 112 is disposed intermediate the bottom surface of end plate 132 and the top surface 102 of flange 208. The stem section 103 extends through the hollow threaded flange member 207 and has adjustably affixed thereto a unibal member 108.

A similar structure exists on the upper end plate 133. However, only the undercut ring 104 is secured to end plate 133. The central portion 105 being adapted to receive the flanged portion 106 of the stem member 113, while the stern extension 109 positioned therebetween has a unibal member 2118 adjustably aflixed thereto.

In the first embodiment, the operation is as follows. The complete unit is assembled as shown. If we assume that the load cell 10 is of a particular capacity, the spring assembly is preloaded an equivalent amount. Once the preloadis reached, the load cell will be deflected at the spring rate. Since a particular load will deflect the load cell a predetermined amount, mechanical stops are provided to prevent overload. The stops are in the form of flanges orjamb nuts positioned on the threaded stem 12. Flange 18 in the present instance working'in cooperation withtheadjustable plug 40 limits the load cell movement in tension, while jamb nut 16 cooperates with plug 40 to limit the movement of the load cell in compression. The

graph illustrated in FIG. 4 shows a typical load deflection curve with and without the present invention. Line A indicates a typical load cell deflection curve, while line B indicates the deflection curve when the present invention is applied. Adjustment of the system is made through rotation of plug 40 and jamb nuts 14 and 16.

The embodiment illustrated in FIG. 2 operates in the same fashion. The load cells 110 and 111 in this case being of different capacities. The preloaded spring units 128 and 1-29 in effect are individual assemblies, each of which is preloaded to cooperate with a particular capac- 4 ity load cell. Mechanical stops 101 and 208 are provided in the lower load cell for limiting movement of the flanged stem member '112. Adjustment in the system is made by rotation of the flanged stop member 207.

On the upper unit, mechanical stops are provided by the end of member- 133 and the inside undercut face of ring member 104. Engagement of the flange 106 with these surfaces limits the movement thereof. One surface limiting the movement in tension, while the other surface limits the movement in compression. The ball bushing maintaining both assemblies in alignment.

Should it be found necessary to use only one load cell in the tandem device, the flanged member 207 is rotated to render movement ofload cell inoperable.

An individual preloaded spring assembly 324 can be used in cooperation with a separable load cell 310 as shown in FIG. 5. In this structure, mechanical stops 315 are provided to limit movement of the unit.

Having thus described my invention, I claim:

1. In an overload protector for limiting the force applied to a load cell, the combination of a force measuring load cell; an unyielding housing around said load cell; a hollow flanged cylindrical member secured to said load cell; the flange on said hollow member has positioned thereon a pair of circular rings; retainer means for retention of said rings; a plurality of preloaded compression springs positioned in spaced relationship intermediate said pair of rings; stop means on said housing for engagement with said circular rings; additional stop means on said housing for limiting compression of said springs upon application of a load.

2. A device as in claim 1 wherein the compression springs are piloted to prevent cocking.

31A device as in claim 1, wherein a double row of springs are used..

4. A device as in claim 1 wherein two compression springs are nested together on the pilot.

5; A device as in claim 1 wherein the spring pilots are located on the retainer.

6. A device as in claim 1 wherein two similar assemblies are joined together, one of high load capacity, one

of low load capacity; and pilot means positioned in said hollow flanged cylindrical members for axial alignment of the-two assemblies.

7. A preloaded spring device having a housing forming an outer body; an upper and lower retainer flange on said housing outer body; an inner flanged body positioned in spaced relationship with said outer body; a pair of axially positioned rings on said inner flanged housing; a plurality of compression springs located between the rings; retainer means for holding and preloading said springs; and mechanical stop means on said housing for limiting compression of said springs upon application of a load; said device to be used in connection with a separable load cell.

8. A device as in claim 1 wherein the springs are piloted on the spring ring proper.

References Cited in the file of this patent UNITED STATES PATENTS 1,580,430 Gaines Apr. 13, 1926 2,170,197 Gumprich Aug. 22, 1939 2,421,222 Schaevitz' May 27, 1947 2,616,683 Le Fevre Nov. 4, 1952 2,720,111 Clark Oct. 11, 1955 

1. IN AN OVERLOAD PROTECTOR FOR LIMITING THE FORCE APPLIED TO A LOAD CELL, THE COMBINATION OF A FORCE MEASURING LOAD CELL; AN UNYIELDING HOUSING AROUND SAID LOAD CELL; A HOLLOW FLANGED CYLINDRICAL MEMBER SECURED TO SAID LOAD CELL; THE FLANGE ON SAID HOLLOW MEMBER HAS POSITIONED THEREON A PAIR OF CIRCULAR RINGS; RETAINER MEANS FOR RETENTION OF SAID RINGS; A PLURALITY OF PRELOADED COMPRESSION SPRINGS POSITIONED IN SPACED RELATIONSHIP INTERMEDIATE SAID PAIR OF RINGS; STOP MEANS ON SAID HOUSING FOR ENGAGEMENT WITH SAID CIRCULAR RINGS; ADDITIONAL STOP MEANS ON SAID HOUSING FOR LIMITING COMPRESSION OF SAID SPRINGS UPON APPLICATION OF A LOAD. 